CDN not used on some pages

We’ve been using the CDN plugin and KeyCDN for quite a while and had no issues. Whilst going through a testing cycle, we’ve discovered that when a product on a Woocommerce product page is added to cart, the page returned doesn’t use the CDN. All links for static content; CSS, JS, and images are to the “www” subdomain for the site, and not the “static” subdomain that we use for the CDN. So far we’ve not seen the issue on other pages.